Split-brain research into hemispheric lateralisation

• Split-Brain Research into hemispheric lateralisation

  Hemispheric lateralisation

  The idea that the two halves of the brain are functionally different and that certain mental processes and behaviours are mainly controlled by one hemisphere rather than the other.
• Split-Brain Research into hemispheric lateralisation 2

  Split Brain studies

  Sperry's (1968) studies involved a unique group of individuals, all whom had undergone a commissurotomy in which the corpus callosum was severed in order to separate the two hemispheres and control frequent and severe epileptic seizures. main communication line between hemispheres was removed which allowed Sperry and colleagues to see extent to which two hemispheres were specialised for certain functions, and whether they performed tasks independently from one another.
• Split-Brain Research into hemispheric lateralisation 3

  Procedure

  Sperry devised general procedure in which an image/word could be projected to individual's right visual field (processed by left hemisphere) and the same/diff image could be projected to the left visual field (processed by right hemisphere). Meant info could not be conveyed from that hemisphere to the other.
• Split-Brain Research into hemispheric lateralisation 4

  Key findings

  Describing what you see - When picture of an object was shown to an individuals right visual field, could easily describe. But if shown to left visual field, could not describe what was seen/reported there was nothing there. For most people, language is processed in left hemisphere. Thus, inability to describe objects in left visual field was cos of lack of language centres in right hemisphere. In a normal brain, messages from right hemisphere would be relayed to language centres of left hemisphere.
• Split-Brain Research into hemispheric lateralisation 5

  Key findings 2

  Recognition by touch - Although could not attach verbal labels to objects projected in left visual field, were able to select matching object from grab-bag of diff objects w/ left hand (linked to right hemisphere). Could not verbally identify but could understand what the object was using the right hemisphere.
• Split-Brain Research into hemispheric lateralisation- evaluation

  Demonstrated lateralised brain functions. Sperry's pioneering working produced impressive and sizeable body of research findings, main conclusion being left hemisphere is geared towards analytic and verbal tasks (analyser) whilst right is more adept at performing spatial tasks and music (synthesiser). Key contribution to our understanding of brain processes.
• Split-Brain Research into hemispheric lateralisation- evaluation 2

  Experiments made use of highly specialised and standardised procedures. Ppts asked to stare at fixation point and image was flashed for one-tenth of a second, meaning split-brain individuals would not have time to move eyes across and spread info across both visual fields, subsequently both hemispheres. Allowed Sperry to vary aspects of procedure while ensuring only one hemisphere was receiving info at a time. Thus his methodology developed useful, well-controlled procedure.
• Split-Brain Research into hemispheric lateralisation- evaluation 3

  Issues with generalisation. Split-brain individuals constitute as an unusual sample of people. Only 11 took part in all variations of basic procedure, all whom had a history of epileptic seizures. Has been argued this may have causes unique changes in the brain that may have influenced the findings. Also some ppts had experienced more disconnection of the two hemispheres.